Photocycloadditions of p-quinones to ketenimines

Abstract

Photo-induced cycloadditions of p-benzoquinone derivatives and 1,4-naphthoquinone to several ketenimines afforded 1 : 1 adducts. Two consecutive adducts, 2-imino-1-oxaspiro [3.5] nona-5,8-dien-7-ones and 1-aza spiro[3.5]nona-5,8-diene-2,7-diones, were obtained from these photolyses in moderate yields. Their structures, which had been postulated as intermediates in a similar reaction, were determined by physical and chemical methods. These two types of spiro-cyclohexa-2,5-dienone gave the rearranged products, 2,3-dihydro-5-hydroxy benzofuran-2-imines and 5-hydroxyindolin-2-ones, respectively, by Lewis-acid catalysed rearrangement.